1 /* 2 * Distributed under the Boost Software License, Version 1.0. 3 * (See accompanying file LICENSE_1_0.txt or copy at 4 * http://www.boost.org/LICENSE_1_0.txt) 5 * 6 * Copyright (c) 2020 Andrey Semashev 7 */ 8 /*! 9 * \file atomic/detail/gcc_atomic_memory_order_utils.hpp 10 * 11 * This header contains utilities for working with gcc atomic memory order constants. 12 */ 13 14 #ifndef BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_ 15 #define BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_ 16 17 #include <boost/memory_order.hpp> 18 #include <boost/atomic/detail/config.hpp> 19 #include <boost/atomic/detail/header.hpp> 20 21 #ifdef BOOST_HAS_PRAGMA_ONCE 22 #pragma once 23 #endif 24 25 namespace boost { 26 namespace atomics { 27 namespace detail { 28 29 /*! 30 * The function converts \c boost::memory_order values to the compiler-specific constants. 31 * 32 * NOTE: The intention is that the function is optimized away by the compiler, and the 33 * compiler-specific constants are passed to the intrinsics. Unfortunately, constexpr doesn't 34 * work in this case because the standard atomics interface require memory ordering 35 * constants to be passed as function arguments, at which point they stop being constexpr. 36 * However, it is crucial that the compiler sees constants and not runtime values, 37 * because otherwise it just ignores the ordering value and always uses seq_cst. 38 * This is the case with Intel C++ Compiler 14.0.3 (Composer XE 2013 SP1, update 3) and 39 * gcc 4.8.2. Intel Compiler issues a warning in this case: 40 * 41 * warning #32013: Invalid memory order specified. Defaulting to seq_cst memory order. 42 * 43 * while gcc acts silently. 44 * 45 * To mitigate the problem ALL functions, including the atomic<> members must be 46 * declared with BOOST_FORCEINLINE. In this case the compilers are able to see that 47 * all functions are called with constant orderings and call intrinstcts properly. 48 * 49 * Unfortunately, this still doesn't work in debug mode as the compiler doesn't 50 * propagate constants even when functions are marked with BOOST_FORCEINLINE. In this case 51 * all atomic operaions will be executed with seq_cst semantics. 52 */ convert_memory_order_to_gcc(memory_order order)53BOOST_FORCEINLINE BOOST_CONSTEXPR int convert_memory_order_to_gcc(memory_order order) BOOST_NOEXCEPT 54 { 55 return (order == memory_order_relaxed ? __ATOMIC_RELAXED : (order == memory_order_consume ? __ATOMIC_CONSUME : 56 (order == memory_order_acquire ? __ATOMIC_ACQUIRE : (order == memory_order_release ? __ATOMIC_RELEASE : 57 (order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_SEQ_CST))))); 58 } 59 60 } // namespace detail 61 } // namespace atomics 62 } // namespace boost 63 64 #include <boost/atomic/detail/footer.hpp> 65 66 #endif // BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_ 67